Executive Board

Understanding superflow dynamics in the presence of impurities is crucial for explaining phenomena in high-Tc superconductors and neutron stars. Ultracold atomic gases offer a versatile platform to study superfluid transport, particularly in ring-shaped traps where

persistent currents arise with quantized circulation determined by the winding number. Here, we examine the role of impurities on the persistent current stability, critical current and vortices mobility, from molecular Bose-Einstein condensate (BEC) to Bardeen-

Cooper-Schrieffer (BCS) superfluids. We find that in the BEC limit increased impurities density stabilizes the superflow by reducing velocity below a critical threshold, enhancing so the critical winding number. This behavior is confirmed by experimental observations. In contrast, the BCS regime reveals a different story: the current stabilization by impurities is intrinsically limited by the

pair-breaking threshold. Below this value, impurities enhance winding number stability, but pair-breaking continues to drive flow dissipation. Beyond this threshold, superflow destabilizes, emitting vortices. Impurities then govern vortex mobility and pinning, exhibiting regimes of collective pinning and hopping. Notably, pinned vortices in BCS superfluids don't guarantee dissipationless flow due to ongoing pair-breaking. Our findings illuminate the complex interplay between impurities, superfluid nature, and vortex dynamics, advancing our understanding of quantum fluids, with potential applications in quantum technologies.